This invention relates to synchronous detectors for double-sideband amplitude-modulated waves, which have improved signal-to-noise ratios over detectors of the prior art.
In synchronous detectors of the prior art sampling of the modulated carrier takes place at the carrier frequency only, whereas in apparatus according to this invention short samples are taken at a frequency equal to the carrier frequency divided by an integer, at a frequency greater than the Nyquist frequency for the modulating wave, centered on approximate instants of carrier peaks, and the samples are reconstructed in a filter with its high cut-off frequency substantially equal to the highest modulating frequency.